Generally, there are many kinds of key units for the keyboard; such conventional key units either cause inaccurate touch and conduction, or cause no sound indication upon hitting the key top. All such drawbacks of a key unit can more or less cause inconveniences to a user. Currently, there is an improved key unit (a mechanical type), but it includes many complicated parts aside from the high cost thereof. The drawbacks of the aforesaid key units are described further as follows:
(1). Resilient rubber type: this is a push button made of a resilient rubber similar to that of a telephone set; when it is used to key in a letter or the like, it makes no sound to indicate the conduction condition and also has no affirmative hit feeling. Further, after this type of key unit is used for a given period of time, the unit becomes unserviceable as a result of the rubber being hardened or damaged, i.e., the key unit is unable to revert to its normal position and resilient condition. Usually, when one key unit is out of order, it can not be replaced by a new one and the whole keyboard has to be replaced. It is deemed an inconvenient drawback for such equipment.
(2). Spring type: It is a key unit, in which a small spring is installed between the key top and the keyboard plate for providing a resilient force, but it is not a good design because the key top can start swinging. Since the distance from the key top to the conductive points is slightly long, more hitting force from a finger has to be applied before a letter or the like is keyed in. Moreover, the hit feeling is not certain because it makes no sound. In the event of keying in given information, some information might be missed because of there is no hit feeling and the keying speed might be slowed.
(3). Mechanical type: This is shown in FIG. 1, which is a reverse disassembled view of a mechanical keyboard, including a key top 7, a spring 6, a keyboard plate 9, and a key-supporting assembly 1 with a top cap 1A. The key-supporting assembly 1 includes a bottom cap 1B, a base plate 9'; the spring 6 is used for providing the key top with a given resilient force. The key-supporting assembly 1 includes a top cap 1A, a bottom cap 1B, a pushing unit 2, a small spring 3, two metal pieces 8, and a leaf spring 5. After the aforesaid parts are assembled together, the pushing unit 2 will protrude out of the top cap 1A and out of the keyboard plate 9 so as to be mounted under the key top 7; the spring 6 is mounted between the pushing unit 2 and the key top 7 so as to provide a resilient force and a "hit" feeling with a sound. However, it does like the aforesaid two types of key units to be turned on immediately upon being hit. Furthermore the conduction and buffer structure are complicated and expensive. It can provide the aforesaid function, but it would waste considerable time and man-power being assembled, i.e., its manufacturing cost is high, and the maintenance thereof is rather difficult because of the complicated structure. Another drawback of that mechanical type of key unit is that it is too sensitive, and is subject to causing error upon being hit incorrectly. When the spring type of key unit is used for keying in documents or data the user can feel nervous trying to avoid mis-hitting the key. After a long time using that type of keyboard, the user can suffer from occupational maladies such as numb fingers, tendinitis and sore shoulders etc.